PYRIMIDINES 93 



Nucleic acids are white amorphous substances containing 9 to 10 per cent, 

 phosphorus. According to Schmeideberg, the composition corresponds to 

 C 40 H 56 N U O 16 2P 2 O 5 . Nucleic acids give none of the protein reactions. They 

 are precipitated, however, by tannic acid, picric acid, and phosphotungstic 

 acid. They are, therefore, basic besides being acids. Nucleic acids combine 

 with proteins in water and in dilute hydrochloric acid to form difficultly 

 soluble combinations which in some measure have the character of acids and 

 form soluble salts with alkalies. The alkali salt of a combination of nucleic 

 acid and a histone is the nucleohistone of the thymus gland. 



On boiling of nucleic acids with strong acids the purine bases are split 

 off, leaving a substance known as nucleotinic acid. On boiling with strong 

 sulphuric acid this is split into the pyrimidine bases, carbohydrate (pen- 

 toses) and phosphoric acid. 



Nucleic acid 

 treated with strong acids 



Nucleotinic acid Purine bases 



on boiling with 30 per cent, sulphuric acid 



Pyrimidines, pentoses, and phosphoric acid 



The structure of nucleic acid is then extremely complex. For the tritico- 

 nucleic acid of the wheat embryo, T. B. Osborne has suggested the following 

 formula where X is an unresolved residue. 



HO pentose X OH guanine (purine base) 



\/ I ' I / 



P -O - P - O -P-O- P pentose 



/\ l\ l\ \ 



HO pentose OH uracil OH uracil OH adenine (purine base) 



(pyrimidine 

 base) 



Pyrimidines. The mother substance of the pyrimidine bases in the nucleic 

 acid is pyrimidine. The skeleton structure of the pyrimidine is a ring con- 

 sisting of the elements of a molecule of urea and closed with three carbon atoms. 

 The elements of the ring are numbered to determine the position of substituted 

 radicals in the compounds derived from pyrimidine. 



'N-C 6 N = CH 



2 C C 5 HC CH 



3 N-C* N-CH 



Pyrimidine ring. Pyrimidine. 



